The present application claims priority to U.S. Application No. 61/583,729 filed Jan. 6, 2012. The priority application is hereby incorporated by reference in its entirety into the present application.
Heat engines are used to convert thermal energy into useful mechanical work and are often used in power generation plants. One common example of a heat engine is an expander-generator system, which generally includes an expander (e.g., a turbine) rotatably coupled to a generator or other power generating device. As working fluids are expanded in the expander, the shaft connecting the turbine and generator rotates and generates electricity in the generator.
Most power plant expander-generators are based on the Rankine cycle and obtain high temperature/pressure working fluids to expand through the combustion of coal, natural gas, oil, and/or nuclear fission. Typical working fluids for Rankine cycles include water (steam) and air. Recently, however, due to perceived benefits in terms of hardware compactness, efficiency, heat transfer characteristics, etc., there has been considerable interest in using super-critical carbon dioxide (ScCO2) as a working fluid for certain expander-generator applications. Notable among such applications are nuclear, solar, and waste heat energy conversion cycles. Most practical waste heat recovery applications using ScCO2, however, end up with a problematic combination of high pressure and relatively high temperature working fluids that are difficult to effectively contain.
One common solution to contain the high pressure and high temperature fluids is installing the expander flowpath components in an unsplit pressure-containing barrel casing. In a typical barrel casing configuration, the internal components are mutually aligned with each other, both axially and radially, by concentric circumferential fits against the inner surface of the barrel casing. This solution is effective for high pressure applications, but only for modest temperatures (e.g., below 600° F.). At higher temperature conditions, the barrel casing design becomes problematic because of non-uniform thermal growth and relative movement of the different internal components inside the casing, as well as movement of the barrel casing itself. These are all the result of potentially significant differences in temperature between components. Consequently, traditional barrel casing mounting often leads to unwanted misalignment, rubbing, and/or binding of stationary and static flowpath components in both transient (i.e., startup, shutdown, and load-change conditions) and steady-state operating conditions.
What is needed, therefore, is a system and method that allows for both high pressure containment in expander-generators, and alignment and ease of adjustment of the internal components for higher temperature applications.